#include <GL/glut.h>
#define window_width  640
#define window_height 480
// Main loop
void main_loop_function() {
    // Z angle
    static float angle;
    // Clear color (screen)
    // And depth (used internally to block obstructed objects)
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    // Load identity matrix
    glLoadIdentity();
    // Multiply in translation matrix
    glTranslatef(0, 0, -10);
    // Multiply in rotation matrix
    glRotatef(angle, 0, 0, 1);
    // Render colored quad
    glBegin(GL_QUADS);
    glColor3ub(255, 000, 000);
    glVertex2f(-1, 1);
    glColor3ub(000, 255, 000);
    glVertex2f(1, 1);
      glColor3ub(000, 000, 255);
      glVertex2f(1, -1);
      glColor3ub(255, 255, 000);
      glVertex2f(-1, -1);
      glEnd();
      // Swap buffers (color buffers, makes previous render visible)
      glutSwapBuffers();
      // Increase angle to rotate
      angle += 0.25;
  }
  // Initialze OpenGL perspective matrix
  void GL_Setup(int width, int height) {
      glViewport(0, 0, width, height);
      glMatrixMode(GL_PROJECTION);
      glEnable(GL_DEPTH_TEST);
      gluPerspective(45, (float) width / height, .1, 100);
      glMatrixMode(GL_MODELVIEW);
  }
  // Initialize GLUT and start main loop
  int main(int argc, char** argv) {
      glutInit(&argc, argv);
      glutInitWindowSize(window_width, window_height);
      glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
      glutCreateWindow("GLUT Example!!!");
      glutIdleFunc(main_loop_function);
      GL_Setup(window_width, window_height);
      glutMainLoop();
  }
